The structure of the hub motor is as shown in the figure below, and is composed of a rotor, a bearing, a stator, a power and control electronic module, and a sealing back plate.
So what are the technical difficulties affecting the commercial application of hub motors? The main points are as follows:
Electronic differential control technology
Since the electric motor driven by the hub motor cancels the mechanical transmission part of the conventional automobile, it is impossible to use the mechanical differential to perform differential control on the electric motor driven by the hub motor. Although an electronic differential is now available, when the vehicle speed exceeds a certain value At the time, the vehicle will show a significant direction of instability. At present, domestic and foreign companies have initially accumulated proprietary technology in this area.
Intelligent energy management system
In layman's terms, this is a question that 1+1 and so on are not equal to 2. People's expectations are undoubtedly 2 (algebraic sum), but the actual effect can only be less than, at best close to 2 (vector sum). Taking into account the power and energy requirements of all aspects of the vehicle, this constitutes the optimal scheduling and management problem for limited onboard energy and power, or called an intelligent energy management system. It is not only an optimal technical solution for system engineering, but also very difficult to start from the rational allocation and management of the energy of each hub motor, and can include energy feedback considerations.
Reduced unsprung mass of hub motor
Since the driving motor, the speed reduction mechanism and the brake are all concentrated in the wheel by the wheel hub motor, if the effective measures are not taken, the quality of the unsprung mass of the car will increase, and the vibration of the vertical direction of the electric motor driven by the hub motor will be increased. The amplitude affects the adhesion of the tire, which is not conducive to the control of the car, and also reduces the ride comfort and comfort of the car. At the same time, the motor is placed inside the wheel and the motor will withstand the large impact loads from the road surface. Therefore, it is of great significance to study the method of reducing the non-sprung mass of the hub motor to guide the design, structural improvement and theoretical analysis of the electric wheel.
Solutions that reduce the quality of unsprung loads typically include:
1 The unsprung mass is converted to sprung mass by a special form of motor. For example, Johansen, Yang et al. proposed a method for converting the stator mass of a motor into a sprung mass by a special planar motor design.
2 Using the motor mass to construct the vibration absorber to control the negative effect of the vertical vibration caused by the unsprung mass. For example, Nagaya uses motor mass construction shock absorbers to control the negative effects of vertical vibration induced by unsprung mass.
3 Change the ratio of sprung mass to unsprung mass. For example, B.Hredzak et al. designed a hub motor that uses a disc motor. As shown in the figure, the disc motor is composed of a double stator and a rotor, and the two stators are fixed on the chassis to make it a sprung mass, and the rotor is connected with the wheels to drive the wheels to rotate, so that only the rotor portion of the motor is On the wheel. This arrangement of the motor results in a reduction in the unsprung mass compared to the way the entire motor is placed in the wheel. However, this type of drive brings a new problem: the ground impact of the wheel is directly transmitted to the rotor of the motor, which in turn causes the air gap width of the motor to constantly change, affecting the output of the motor torque.
